Option Explicit
Dim FSO As Object, oFolder As Object, StrFolds As String
 
Sub Main()
Application.ScreenUpdating = False
Dim TopLevelFolder As String, TheFolders As Variant, aFolder As Variant, i As Long
TopLevelFolder = GetFolder
StrFolds = vbCr & TopLevelFolder
If FSO Is Nothing Then
  Set FSO = CreateObject("Scripting.FileSystemObject")
End If
'Get the sub-folder structure
Set TheFolders = FSO.GetFolder(TopLevelFolder).SubFolders
For Each aFolder In TheFolders
  RecurseWriteFolderName (aFolder)
Next
'Process the documents in each folder
For i = 1 To UBound(Split(StrFolds, vbCr))
  Call UpdateDocuments(CStr(Split(StrFolds, vbCr)(i)))
Next
Application.ScreenUpdating = True
End Sub

Sub RecurseWriteFolderName(aFolder)
Dim SubFolders As Variant, SubFolder As Variant
Set SubFolders = FSO.GetFolder(aFolder).SubFolders
StrFolds = StrFolds & vbCr & CStr(aFolder)
On Error Resume Next
For Each SubFolder In SubFolders
  RecurseWriteFolderName (SubFolder)
Next
End Sub
 
Function GetFolder() As String
Dim oFolder As Object
GetFolder = ""
Set oFolder = CreateObject("Shell.Application").BrowseForFolder(0, "Choose a folder", 0)
If (Not oFolder Is Nothing) Then GetFolder = oFolder.Items.Item.Path
Set oFolder = Nothing
End Function

Sub UpdateDocuments(oFolder As String)
Dim strFldr As String, strFile As String, wdDoc As Document
strFldr = oFolder: If strFldr = "" Then Exit Sub
strFile = Dir(strFldr & "\*.doc", vbNormal)
While strFile <> ""
  If UBound(Split(strFile, ".doc")) = 0 Then
    Set wdDoc = Documents.Open(FileName:=strFldr & "\" & strFile, AddToRecentFiles:=False, ReadOnly:=False, Visible:=False)
    With wdDoc
      'Save as docx or docm, depending on whether the file contains macros.
      If .HasVBProject = False Then
        .SaveAs2 FileName:=.FullName & "x", FileFormat:=wdFormatXMLDocument, AddToRecentFiles:=False
      Else
        .SaveAs2 FileName:=.FullName & "m", FileFormat:=wdFormatXMLDocumentMacroEnabled, AddToRecentFiles:=False
      End If
      'close the document
      .Close False
    End With
    'Delete the old file
    Kill strFldr & "\" & strFile
  End If
  strFile = Dir()
Wend
Set wdDoc = Nothing
End Sub